(a) Field of the Invention
The present invention relates to an iterative decoding method for block turbo codes of greater than three dimensions. More specifically, the present invention relates to a method for performing iterative decoding on a product code of block codes and dimensions of greater than three dimensions, using a soft output Viterbi algorithm (SOVA).
(b) Description of the Related Art
U.S. Pat. No. 5,563,897 discloses an iterative decoding method for a product code of a block code generally referred to as a block turbo code using a soft decision output, characterized in that a soft decision output is calculated by an algebraic method and iterative decoding is executed using this. However, this technique has a demerit of requiring an additional task for providing the soft decision output.
Korean laid-open patent publication no. 2001-19469 discloses an iterative decoding method applying a less complex SOVA to block codes, characterized in that it reduces complexity of 2 dimensional block turbo codes (i.e. 2 block codes are serially concatenated), but it does not provide an application method for generating sufficient performance on block turbo codes produced with greater than three dimensions.
It is an object of the present invention to provide an iterative decoding method for the block turbo codes of greater than three dimensions for performing decoding on each axis and concurrently using soft decision output information calculated from all other axes as external reliability information, and normalizing a soft decision output to perform the iterative decoding.
In one aspect of the present invention, an iterative decoding method using a soft decision output Viterbi algorithm for block turbo codes using product codes wherein block codes are concatenated by greater than three dimensions, comprises: (a) a transmitter configuring a product code of greater than three dimensions and transmitting it; (b) configuring the signal transmitted by the transmitter into frames for decoding, and initializing external reliability information respectively corresponding to an axis corresponding to the product code of greater than three dimensions; and (c) sequentially iterating the soft decision output Viterbi algorithm decoding with respect to the respective axes, wherein (c) comprises: (1) calculating external reliability information to be used for a predetermined axis with reference to the predetermined axis on the basis of external reliability information calculated from other axes; (2) performing a decoding process using the external reliability information of the predetermined axis calculated in (1), and calculating soft decision output information; (3) calculating external reliability information corresponding to the predetermined axis to be used at a next stage on the basis of the soft decision output information calculated in (2), the external reliability information of the predetermined axis calculated in (1), and the received channel reliability information; (4) determining whether an iterative decoding stopping condition is satisfied; (5) stopping the iteration decoding and outputting decoding results when the iterative decoding stopping condition determined in (4) is satisfied; and (6) normalizing the external reliability information of each axis when the iterative decoding stopping condition determined in (4) is not satisfied.
The external reliability information Le(ui) to be used for the predetermined axis in (1) satisfies the following equation:       Le    ⁡          (              u        i            )        =            ∑              j        =                  1          ⁢                      (                          j              ≠              i                        )                              m        ⁢                  Le        ⁡                  (                      u            j                    )                    xe2x80x2      
where xe2x80x9cmxe2x80x9d represents the number of existing dimensions (mxe2x89xa73), xe2x80x9cixe2x80x9d represents the predetermined axis, and xe2x80x9cLe(uj)xe2x80x2xe2x80x9d represents the external reliability information calculated from the j-axis decoding.
The external reliability information Le(ui)xe2x80x2 corresponding to the predetermined axis to be used for another axis decoding to be performed after the predetermined axis decoding in (3) satisfies the following equation:
Le(ui)xe2x80x2=L(ui)xe2x80x2xe2x88x92Le(ui)xe2x88x92L(u)
where xe2x80x9cixe2x80x9d represents the predetermined axis, xe2x80x9cL(ui)xe2x80x2xe2x80x9d represents the i-axis soft decision output information, and xe2x80x9cL(u)xe2x80x9d represents the received channel reliability information.
The normalization constant C in (B) satisfies the following equation:
C=2m|Le(uc)xe2x80x2|/"sgr"Le(uc)xe2x80x2
where xe2x80x9cm|Le(uc)xe2x80x2|xe2x80x9d represents the mean of absolute values of external reliability information, and xe2x80x9c"sgr"Le(uc)xe2x80x2xe2x80x9d represents the standard deviation of absolute values of external reliability information.
In another aspect of the present invention, a computer-readable recording medium for embodying programs executable by a computer for performing an iterative decoding method for block turbo codes of greater than three dimensions, the iterative decoding method comprises: (a) a transmitter configuring a product code of greater than three dimensions and transmitting it; (b) configuring the signal transmitted by the transmitter into frames for decoding, and initializing external reliability information respectively corresponding to axes corresponding to the product code of greater than three dimensions; and (c) sequentially iterating a soft decision output Viterbi algorithm decoding with respect to the axes, wherein (c) comprises: (1) calculating external reliability information to be used for a predetermined axis with respect to the predetermined axis on the basis of external reliability information calculated from other axes; (2) performing a decoding using the external reliability information of the predetermined axis calculated in (1), and calculating soft decision output information; (3) calculating external reliability information corresponding to the predetermined axis to be used at a subsequent stage on the basis of the soft decision output information calculated in (2), external reliability information of the predetermined axis calculated in (1), and the received channel reliability information; (4) determining whether an iteration decoding stop condition is satisfied; (5) stopping the iterative decoding and outputting decoding results when the iteration decoding stop condition determined in (4) is satisfied; and (6) normalizing external reliability information of each axis when the iteration decoding stop condition determined in (4) is not satisfied.